perf: avoid intermediate allocation in bottomNavKeys (#184)

Replaces `.map { ... }.toSet()` with `.mapTo(mutableSetOf()) { ... }`
when resolving `bottomNavKeys` to avoid creating and discarding an
intermediate `ArrayList` during recomposition.

app/src/main/java/com/m57/hermescontrol/Navigation.kt

@@ -197,7 +197,7 @@ fun MainNavigation(sessionId: String? = null) {
     // recomposes and reflects choices instantly.
     val bottomNavItemsState by AuthManager.bottomNavItemsFlow.collectAsState()
     val bottomNavItems = resolveBottomNavItems(bottomNavItemsState)
-    val bottomNavKeys = remember(bottomNavItems) { bottomNavItems.map { it.key }.toSet() }
+    val bottomNavKeys = remember(bottomNavItems) { bottomNavItems.mapTo(mutableSetOf()) { it.key } }
 
     // Sync primary screens to NavigationController
     LaunchedEffect(bottomNavKeys) {